(1) Field of the Invention
The present invention relates to an improved cutting tool for rotary cutting. In particular, the present invention relates to a cutting tool having a seat with a visual wear indicator. Due to the nature of cutting tools, the cutting insert which is used to machine the workpiece disintegrates during the machining process. As the cutting tool crumbles, the seat on which the cutting insert is positioned comes in contact with the workpiece and is eventually worn down. The cutting insert is expected to disintegrate and thus, is easily removed and replaced in the holder. The seat is also easily removed and replaced in the holder if damaged during the machining process. Furthermore, the cutting insert and the seat are relatively inexpensive and thus replacement of either one is accepted. If the cutting tool is left unattended, however, the seat will completely wear away which will allow the workpiece to make contact with the holder. Damage to the holder is unacceptable as replacing the holder is not as simple or as inexpensive as replacing the cutting insert or the seat. Thus, contact between the holder and the workpiece must be prevented. To solve this problem, a wear indicator is provided as part of the seat or alternately as part of the cutting insert. Contact between the workpiece and the wear indicator creates sparks which alert the user that the seat or cutting insert is disintegrating, thus enabling the user to shut down the machine before the holder is damaged.
(2) Prior Art
The prior art has described various cutting tools of different configurations and utilizing different materials to comprise the cutting tip and the seat. The prior art patents utilized different materials within the seat, cutting insert and holder in order to reduce the stress in the tool or to prevent vibration of the cutting insert within the holder. Illustrative of such patents are: U.S. Pat. Nos. 2,414,231 to Kraus; 2,982,008 to Facknitz; 3,060,554 to Kirchner; 3,246,382 to Zierden; 3,487,514 to O'Brien; 3,577,618 to Cashman; and 5,193,945 to Nakayama.
Kraus describes a cutting tool wherein the tip is comprised of two layers, a thin layer of a situated carbide forming the cutting surface and a thicker under layer of a material also possessing red hardness and constructing a support for the thin carbide layer. The thicker under layer made from the group of the cast nonferrous alloys facilitates grinding of the tip.
Facknitz describes a cutting tool holder which releasably holds a removable cutting insert having a seat which makes possible the adaption of a single cutting tool holder for a variety of sizes of cutter inserts.
Kirchner describes a cutting tool mounting wherein the tip of the cutting tool is of a different material and exhibits appreciably different thermal expansion characteristics than the material of which the holder or mounting for the cutting tool is formed. The different thermal expansion characteristics of the holder and the cutting tool ensure that when cold, the cutting tool is easily removed from the holder and yet when hot, the cutting tool is held securely within the holder.
Zierden describes a cutting tool wherein the holder and the seat member have been provided with "through pass" machining which permits grinding both the vertical and horizontal surfaces of both the holder and the seat member to any desired degree of planeness and angle between surfaces. This machining allows for a better fit between the holder and the seat member.
O'Brien describes a cutting tool wherein an intervening metal section having a low coefficient of thermal expansion is provided between the ceramic cutting tip and the steel holder. The metal section reduces the inherent stresses of the cutting tip and the steel resulting from the bonding of the materials by brazing.
Cashman describes a tool holder which supports the removable tool bit in a way which reduces the possibility of vibration of the tool bit.
Nakayama describes a cutting tool wherein the positioning block on which the cutting insert is mounted is comprised of two layers. The first layer is made of a soft material such as to absorb undesirable vibrations and shocks which act on the cutting insert during the milling operation. The second layer is made of a high hardness material and is responsible for preventing the wear of the positioning block.
None of the prior art patents show the use of a wear indicator within the seat or the cutting insert to alert the user prior to contact between the workpiece and the holder.